<html>
<style>
/*
.before:before{content:'you before'; 
color:red;
display:block;}*/
/*
//鼠标移至 div 上时，新内容出现。
*/
.before:hover:before{
	content:'you before'; 
	color:red;
}
a::before{content: attr(title)}

</style>

<div class="before"> me</div>
<a href="http://www.segmentfault.com" title="Jerry Scala"></a>
<script>
</script>

</html>